Compressor surge prevention and drive motor cooling system



Dec. 13, 1960 J. c. BEGGs Erm.

COMPRESSOR SURGE PREVENTION AND DRIVE MOTOR COOLING SYSTEM 2 SheetsSheefl 1 Filed June 19, 1959 Ri l? QN mw.

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Dec. 13, 1960 J. c. BEGGS ET AL 2,963,378

COMPRESSOR SORGE PREVENTION AND DRIVE MOTOR COOLING SYSTEM Filed June 19, 1959 2 Sheets-Sheet 2 IN V EN TORS MOH/V C'. 195665 BY FRED M jfA/,BUSH

A WOR/VE YS Attes CONIPRESSOR 'SURGE PREVENTION AND DRIVE MG'IR CULING SYSTEM Filed .lune 19, 1959, Ser. No. 821,440

Claims. (Cl. 62`196) This invention .relates to refrigeration systems and, more particularly, to refrigeration systems of the type which include a refrigerant compressor of the centrifugal type and an electric motor for driving the compressor. In refrigeration systems of this type, and particularly in systems Where refrigerant flow may vary substantially through the compressor, the problem of compressor surge is often encountered. In addition, such systems usually present a drive motor cooling problem.

It is the general object of the present invention to provide, in a refrigeration system of the type mentioned, an auxiliary system adapted to prevent compressor surge and at the same time provide for effective cooling of the compressor drive motor.

The drawings show a preferred embodiment of the invention and such embodiment will be described, but it will be understood that various changes may be made from the construction disclosed, and that the drawings and description are not to be construed as defining or limiting the scope of the invention, the claims forming a part of this specification being relied upon for that purpose.

Of the drawings:

Fig. 1 is a schematic illustration of a surge prevention and motor cooling system forming a preferred embodiment of the invention, the same being shown incorporated in an exemplary refrigeration system adapted for aircraft use.

Fig. 2 is a schematic illustration of a surge prevention and motor cooling system which forms an alternative embodiment of the present invention.

While the exemplary refrigeration system shown in Fig. 1 of the drawing is adapted to cool air supplied to a cabin 10 in an aircraft, it will be obvious that the said system may be utilized for a variety of other cooling purposes. Air is supplied to the cabin 10 in Fig. l from an inlet duct 12 which receives the air from a refrigerant evaporator 14, the evaporator being supplied in turn from an air supply duct 16. The supply duct 16 receives air from a suitable source (not shown) which may comprise a ram air scoop, air recirculated from the cabin or other enclosures in the aircraft, or air bled from the compressor of an aircraft engine.

The evaporator 14 is or may be of conventional construction and has a -first group of passageways for the flow of cabin supply air and a second group of passageways through which the system refrigerant passes in outof-contact heat exchange relationship with the said supply air. As a result of heat exchange in the evaporator, the cabin supply air is suitably cooled and the refrigerant, entering the evaporator in liquid form, is boiled and converted to a superheated vapor. A conventional thermosensitive expansion valve 18 associated with the evaporator 14 regulates the flow of refrigerant therethrough to provide for the discharge of refrigerant from the evaporator at a substantially constant level of superheat.

The discharge side of the evaporator 14 is connected with an inlet conduit 20 for a two-stage centrifugal type e 2,963,878 Patented Dec. 13, 1960 compressor 22 and a discharge conduit 24 for the compressor 22 extends to the inlet side of a refrigerant condenser 26. A connecting conduit 28 extends between the discharge side of the condenser 26 and the inlet side of the evaporator 14 to complete the refrigerant flow circuit. Thus, it will be seen that superheated refrigerant discharged from the evaporator 14 passes through the compressor 22 where it undergoes a pressure and temperature increase and then through the condenser 26 where it is liqueied prior to redelivery to the evaporator. The condenser 26 is or may be of conventional construction and the cooling medium utilized therein in out-ofcontact heat exchange relationship with the refrigerant may be ram air as in a conduit 30.

From the foregoing it will be apparent that the exemplary refrigeration system as thus far generally described is conventional in construction and operation. A detailed description of the refrigeration system is not deemed necessary for a full understanding of the invention, but if such details are desired, reference may be had to the copending application of Coburn et al., Serial No. 778,489, filed December 5, 1958, and entitled Electronic Back Pressure Control.

It will be further apparent from the foregoing that substantial variation in the flow of refrigerant will occur in the exemplary refrigeration system. Variation in the temperature or ow of cabin supply air through the evaporator 14 will cause the expansion valve 18 to adjust the ow of refrigerant through the evaporator in order to maintain substantially constant superheat of the refrigerant at the evaporator discharge side. This, of course, will result in variation in refrigerant flow throughout the system. Moreover, it is to be observed that a valve 32 is disposed in the compressor inlet conduit 20 in the system as shown. The said valve is operable responsive to a temperature sensitive element 34 disposed in the cabin 10 to vary back pressure in the said conduit. In this manner, the expansion valve 18 is caused to vary refrigerant ow through the evaporator whereby to regulate the cabin temperature in a desired manner 0r in accordance with a desired schedule. While the invention does not relate to the details of construction and operation of the valve 32, it is important to observe that refrigerant ow in the refrigeration system is subject to additional variation as a result of the inclusion of the said valve therein. The aforementioned copending application of Coburn et al., may be referred to for a detailed description of the function and operation of a valve such as the valve 32.

As mentioned previously, the present invention is concerned with the prevention of compressor surge and with cooling of a drive motor associated with the compressor. It will be obvious from the foregoing that substantial variation in refrigerant ow may be encountered in the exemplary refrigeration system shown and described and it will be further obvious that there may be conditions of operation wherein the ow of refrigerant through the compressor is suciently reduced to cause compressor surge. This, of course, may be true also of other refrigeration systems Which incorporate refrigerant compressors of the centrifugal type and the invention therefore is not to be construed as limited in its application to the particular refrigeration system shown.

In accordance with the invention, a conduit is provided between the discharge and inlet sides of a centrifugal refrigerant compressor in order to provide for recirculation of a portion of the refrigerant discharged from the compressor. In addition, a valve means is provided in said conduit so that recirculation of the refrigerant may be effected only when required to prevent compressor surge. That is, the said valve means is adapted to regulate refrigerant ow in the recirculation Conduit so that the main flow through the compressor is supplemented as required to prevent compressor surge.

In the embodiment of the invention shown in Fig. l of the drawing, a recirculation conduit 36 is provided and extends between the compressor discharge conduit 2.4. and the compressor inlet conduit 2G, Associated with the recirculation conduit 36 is a valve means indicated generally at 38 which comprises a valve member 40, a pressure responsive valve actuator 42, and an actuator control means 44. The valve member 40 is connected with and moved by an actuator diaphragm 46 which is biased in one direction by a spring 48 and urged in an opposite direction by fluid pressure in a control chamber 50. Movement of the diaphragm 46 in said one direction results in opening movement of the valve member 40 in the recirculation conduit 36 and movement of Said diaphragm in said opposite direction results in closing movement of the said Valve member in said conduit.

The position of the actuator vdiaphragm 46 and thus the position ofthe valve member 4t) in the conduit 36 is controlled by the actuator control means 44. That is, the control means 44 operates to regulate pressure in the actuator control chamber 50 whereby to adjust and control the position of the actuator diaphragm 4.6 and valve member 40. A supply conduit 52 for the actuator control chamber 50 has a small poppet valve 54 associated with its inlet port 64 to regulate flow from a chamber 56 in the control means 44 through said conduit. The chamber 56 is connected with the compressor discharge conduit l24 by a conduit 58 for a supply of superheated refrigerant which is utilized as a servo fluid. Thus, superheated refrigerant may flow from the com pressor discharge conduit 2,4 through the conduit 58, the chamber 56, and the actuator supply conduit 52 to the actuator control chamber 50 under the control of the poppet valve 54. A discharge conduit 60 for the actuator control chamber extends therefrom to the/recirculation conduit 36 and has disposed therein a restriction 62. The restriction 62 in the conduit 60 permits the poppet valve 54 to effect substantial pressure changes in the actuator control chamber 50 without moving comparatively large distances in order to effect excessive changes in the area of the inlet port 64 for the actuator supply conduit 52.

From the foregoing, it will be apparent that the poppet valve 54 may be moved in one direction to slightly increase the area of the inlet port 64 of the conduit 52 whereby to increase pressure in the actuator control chamber and cause the valve member 40 to be moved inthe valve closing direction. lt will be further apparent that the poppet valve 54V may be moved slightly in an opposite direction to decrease the area of said inlet port whereby to decrease actuator control pressure'in the chamber 50 and cause the valve member 40 in the recirculation conduit to be moved in the valve opening direction. e Y 'l Movement of the poppet valve 54 in said one and opposite directions is eifec'ted by a diaphragm 66 included in the control means 44; and connected with said valve. The diaphragm 66 is urged in one direction to move the poppet valve 54 in its said one directonand increase the area of the inlet port 64 by superheatedrefrigerant in a chamber 68. Said refrigerant is substantially `at the total compressor discharge conduit pressure byfreason of the connection of the chamber 68 with a total pressure tap 70 in the compressor discharge conduit 24. A chamber 72 connected with a static pressure tap 74 in the compressor discharge conduit 24 is disposed adjacent the diaphragm 66 on Vthe side opposite thechamber 68. Thus, the diaphragm 656 is urged in an opposite direction to cause the poppet valve 5d to decrease the area ofthe inlet port 64 by superheatedrefrigerant at substantially the compressor .discharge conduit static pressure.

' From the foregoing, it will be apparent that the con- 2,963,878 i u f trol means 44 will operate to adjust actuator control pressure in the chamber 50 as required to position the valve member 40` for an increased ow through the recirculation duct 36 when the compressor discharge flow decreases. Conversely, a decreased flow through the recirculation conduit will be provided when the compressor discharge flow increases. A decrease in flow through the compressor discharge conduit 24 results in a decreased pressure differential across the diaphragm 66 in the control means 44. This causes the said diaphragm and the poppet valve 54 to be moved so that the inlet area of the conduit 52 is decreased. A reduction in pressure in the actuator control chamber 50 results and the valve member 40 is moved in the valve opening direction. An increase in ow through the compressor discharge conduit 24 is accompanied by an increase in the pressure differential across the diaphragm 66. Movement of the poppet valve 54 in the direction whichY increases the opening of the inlet port 64 for the conduit 52 results and an increase in actuator control pressure is effected to cause closing movement of the valve member 40.

In view of the above-described operation of the valve means 44, it will be obvious that proper adjustment of the said valve means will permit the low flow conditions which might result in compressor surge to be avoided. When operating conditions of the refrigeration system are such that compressor discharge ow is reduced sufliciently to cause compressor surge, the valve member 40 will be opened and its position will thereafter be adjusted automatically as required to regulate recirculation flow so as to prevent compressor surge. Other types of valve means may obviously be utilized to control ilow through the recirculation conduit in a similar manner and for the same purpose and, accordingly, it is to be understood that the invention is not limited to the particular recirculation flow control means shown and described.

In further accord with the present invention, a cooling conduit is provided andvis connected with a Source of cooled Aliquefied refrigerant of the type utilized in the refrigeration system. The said cooling conduit is connected with an electric drive motor for the centrifugal compressor and it is also connected with the recirculation conduit in the surge prevention and motor cooling system. Cooled. liquefied refrigerant is thus delivered to the motor wherein it is evaporated and serves to reduce motor temperature and such refrigerant is also utilized to cool or quench refrigerant flowing in the recirculation conduit. Valve means is disposed in the cooling conduit and is adapted to regulate iiow therethrough so that themotor is effectively lcooled and so that the recirculating refrigerant is also cooled as required. As will be seen, the connection of' the cooling conduit with both the motor and the recirculation conduit permits control of the said valve means to be accomplished for both purposes in response to superheat or other conditions in the recirculation conduit. That is, the valve means may be clontrolled in response to superheat or other conditions in the recirculation conduit and the flow of cooled liquefied refrigerant maybe thus established so that the motor is effectively cooled and so that the condition of the recirculating refrigerant is at the same time regulated ina desired manner. l i

in thefembodiment of theY invention shown in Fig. 1, a cooling conduit is indicated generally by the reference numeral'76. The said, conduit comprises first and second portions 78 and 86 whichy extend respectively from the connecting conduit 23 between the evaporator L4 and the condenser, 2-6 tothe fluidftight casing of an electric drive motor 82 and from saidmotor casing to the recirculation conduit 36. Thus, cooled liquefied refrigerant delivered to the conduit '28 bythe condenser 26 is di: rected rst to the interior of the casing of the electric drive motor- 82 where' it is evaporated a'nd'cools the said drive motor. The evaporated refrigerant is then directed to the recirculation conduit 36 wherek it serves to cool' or quenc superheated refrigerant flowing in said recirculation conduit. Recirculating refrigerant may attain excessively high levels of superheat and it is therefore desirable to cool or queue the same as described in order to prevent the re-entry thereof to the compressor 22 in such condition and avoid detrimental effects on the compressor.

Associated with the first portion 78 of the cooling conduit 76 is a valve means 84 which preferably comprises a conventional thermo-sensitive expansion valve. A chamber 86 on one side of a diaphragm 88 in the expansion valve contains a trapped independent quantity of refrigerant of the type utilized in the refrigeration system. The end wall and a portion of the side walls of the said chamber 86 are disposed in the recirculation conduit 36 downstream of the connection of said conduitrwith Vthe second portion 80 of the cooling conduit 76. Thus, the trapped refrigerant in the chamber 86 acts on the diaphragrn 88 to urge the same in one direction with a pressure force determined by the temperature of the refrigerant in the recirculation conduit 36 adjacent said chamber. 'Ihe diaphragm 88 is connected with a valve member 90 by a suitable linkage 92 in such manner that the action of the trapped refrigerant on the diaphragm 88 tends to urge the said valve member in one direction and open an associated port 94 formed in a partition 96 disposed between valve inlet and discharge chambers 98 and 104i. Thus, the pressure of the trapped refrigerant on the diaphragm 88 tends to cause an increase in the flow of refrigerant from the inlet chamber 98 to the discharge chamber 100. The first portion 78 of the cooling conduit 76 is connected with said inlet and discharge chambers so that movement of the valve member 93 in the above-described manner permits an increased iiow of cooled liquefied refrigerant to the drive motor 82.

A pressure chamber 102 in the expansion valve Sli is connected with the recirculation conduit 36 by a conduit 104 and is disposed adjacent the diaphragm 88 on the side opposite the aforementioned chamber 86. Thus, a refrigerant in the recirculating conduit is introduced to the chamber 102 for action on the diaphragm S8 in opposition to the pressure exerted by the trapped refrigerant in the chamber 86. In addition, a superheat spring 106 acts on the valve member 90 to urge the said member and the diaphragm 88 in opposition to the pressure exerted by the refrigerant in the chamber 86.

From the foregoing it will be apparent that the expansion valve 84 will operate to maintain a substantially constant level of superheat of refrigerant in the recirculation conduit 36 downstream of the connection thereof with the second portion 80 of the cooling conduit 76. Under conditions of operation of the refrigeration system wherein the main flow of refrigerant through the compressor 22 is above the level where surge is encountered, the valve member 40 of the valve means 38 will be in its fully closed position and the refrigerant discharged to the recirculation conduit 36 from the motor 82. will constitute the total ow through the said recirculation conduit. In maintaining a substantially constant superheat of such motor discharge refrigerant, the expansion valve 84 will serve to assure effective cooling of the motor and at the same time it will prevent the refrigerant from entering the compressor in an unacceptable condition. That is, the motor discharge refrigerant will not be permitted to enter the compressor at an excessively high level of superheat, nor will the said refrigerant be permitted to enter the compressor in a partially liquefied state such as might result in cavitation of the compressor blades.

Under conditions of refrigeration system operation wherein recirculation of refrigerant is effected by the valve means 38 to prevent compressor surge, the expansion valve 84 will operate to maintain a substantially constant level of superheat of the mixed refrigerant comprising the superheated refrigerant passing the valve member 40 and the evaporated motor discharge refrigerant.

Here again, the introduction of excessively superheated refrigerant or partially liquefied refrigerant to the compressor is prevented. It is to be observed, however, that the overcooling of the motor may be encountered. That is, the valve 84 may be required to provide a flow of refrigerant substantially in excess of that required for cooling the motor in order to accomplish the additional task of cooling or quenching the recirculating refrigerant from the compressor discharge line 24 so as to maintain the desired substantially constant level of superheat of the mixed refrigerant. However, it has been found that such overcooling of the motor, even under the most severe conditions of system operation, does not have any serious detrimental effects thereon.

The surge prevention and cooling system forming the Valternative embodimentVV of the invention and which is shown in Fig. 2, makes use of any available cooling capacity of superheated refrigerant which is recirculated from the outlet to the inlet side of the compressor. That is, the said recirculated refrigerant may, under certain conditions of operation of the refrigeration system, be at a temperature somewhat lower than the compressor drive motor. in order to take advantage of the cooling capacity of the recirculated refrigerant under these conditions of operation, the refrigerant is passed through the drive motor to cool the same. Cooling of the drive motor and quenching of the recirculating refrigerant under other conditions of system operation are provided for in substantially the same manner as is the surge prevention and motor cooling system of Fig. l.

Referring particularly to Fig. 2, it will be observed that a compressor 22a shown therein is provided with an inlet conduit 20a and a discharge conduit 24a. The inlet and discharge conduits 20a and 24a may form a part of a refrigeration system identical with that shown in Fig. l. The compressor 22a is of the centrifugal type and is of two-stage construction as in Fig. l. An electric drive motor 82a, corresponding to the drive motor 82 of Fig. l, is connected with the compressor 22a and requires cooling under certain conditions of refrigeration system operation.

A recirculation conduit 36a, in the alternative surge prevention and motor cooling system, comprises a first portion Seb and a second portion 36o. The first portion 3615 of the recirculation conduit extends between the compressor discharge conduit 24a and the drive motor 82a and is in communication with the interior of the motor casing which is of fluid tight construction. The second portion 36C of the recirculation conduit is also in communication with the interior of the casing of the motor 82a and extends from the said motor to the inlet conduit 20a for the compressor 22a. Thus, refrigerant which is recirculated to the conduit 36a to prevent cornpressor surge passes through the casing of the drive motor 82a and may serve to cool the said motor when its temperature is lower than that of the motor.

In order that a recirculation ow may be provided only when necessary to prevent compressor surge, a valve means 38a is provided. Said valve means comprises a valve member 46a which is adapted to vary flow through the first portion Sb of the recirculation conduit and may be identical with the valve means 38 of Fig. l as shown.

The alternative surge prevention and motor cooling system also includes a cooling conduit 7 6a which is connected with a source of cooled liquefied refrigerant and which is shown as extending from the condenser in the refrigeration system. More specifically, the cooling conduit 76a extends from the condenser or its discharge conduit to the first portion 36h of the recirculation conduit 36a and thus may be described as being in communication (albeit indirectly) with the interior of the casing of the motor ma.

The cooling conduit 76a has associated therewith a valve means 84a which is adapted to regulate refrigerant flow therethrough whereby to provide for effective cooling of the motor 82a and cooling or quenching of the nrecirculating refrigerant in the Conduit 36a as required. The valve means ,84g is preferably a thermo-sensitive eX- pansion valve and may be identical with the valve means v84 of Fig. i as shown. Thus, the said valve means operates to provide for a substantially constant level of superheat in the second portion 36o of the recirculation conduit 36a; the connection of said valve means with said second recirculation conduit portion being substantially identical with the connection of theV valve means 84 with the recirculation conduit 36 in Fig. 1.

From the foregoing, it will -be apparent that recircula` tion of superheated refrigerant will be accomplished as necessary to prevent compressor surge in the alternative system of Fig. 2. When the recirculating superheated refrigerant is at a temperature lower than the temperature of the lmotor 82a, the said motor will be cooledY thereby. When the temperature of ysai-d recirculating lrefrigerant is in excess of the motor temperature, the valve means 84a will operate to introduce sufficient cooled liquefied refrigerant to the first portion 3617 of the recirculation conduit to provide `for cooling of Vthe motor 82a and quenching of the recirculating refrigerant as required. When the valve means 38a operates to interrupt the flow of recirculating refrigerant, the valve means 84a will provide cooled liquefied refrigerant as necessary for cooling the motor.

It will be observed that overcooling of the motor 82a may be encountered in the Fig. 2 system as in the Fig. l system. When the valve means 84a is required to introduce sufficient liquefied refrigerant to cool the motor and, in addition, to quench the recirculating refrigerant, overcooling of the motor may obviously result. It has been found, however, that such overcooling is not accompanied by serious detrimental effects. i

The invention claimed is:

l. In a refrigeration system wherein there is substantial variation in refrigerant flow, the combination of a .centrifugal compressor connected in the system to accommodate -vaporized refrigerant under variable flow conditions, an electric drive motor for the compressor having a iiuidtight casing, a recirculation conduit connected between the outlet and inlet sides of the compressor, valve means in said conduit adapted to provide for recirculation flow of the vaporized refrigerant whereby to supplement the main flow through the compressor as required to prevent compressor surge, and a cooling conduit connected with a Vsource of cooled liquefied refrigerant and communicating with the interior of said motor casing and with said recirculation conduit toV provide for cooling of said motor and of recirculating refrigerant.

2. In a refrigeration system wherein there is substantial variation in refrigerant flow, the combination of a centrifugal compressor connected in the system to accommodate vaporized refrigerant under variable flow conditions, an electric drive motor for the compressor having a fluid-tight casing, a recirculation conduit connected between the outlet and inlet sides of the compressor, valve means in said conduit adapted to provide for recirculation iiow of the vaporized refrigerant whereby to supplement the main ow through the compressor as required to prevent compressor surge, a cooling conduit connected with a source of cooled liquefied refrigerant and communicating with the interior of said motor casing and with said recirculation conduit, and valve means in said cooling conduit adapted to regulate refrigerant flow therethrough to provide for cooling of the motor and cooling of recirculating refrigerant.

3. In a refrigeration system wherein there is substantial variation in refrigerant flow, the combination of a centrifugal compressor connected in the system to accommodate superheated refrigerant under variable flow conditions, an electric drive motor for the compressor having a Huid-tight casing, a recirculation conduit connected between the outlet and inlet sides of the compressor, valve means in .said conduit adapted to provide for recirculation iiow of the superheated refrigerant whereby to supplement the main ,refrigerant HOW through the 'compressor as required to prevent compressi?? Surge, av cooling conduit connected with `a source of cooled Aliquefied refrigerant and communicatingfwith the interiQr of said motor casing and with said recirculation conduit, and valve means in said cooling conduitvadapted to regulate refrigerant iiow therethrough whereby toV provide for the recirculation of refrigerant tofthe compressor at a substantially constant level of superheat.

4. in a refrigeration system wherein there is substantial variation in refrigerant flow, the combination of a centrifugal compressor connected in theV system to accommodate vaporized refrigerant under variable flow conditions, an electric drive motor for the compressor having a fluid-tight casing, a recirculation conduit connected be- Vtween the outlet and inlet sides of the compressor, valve means in said conduit adapted to Vprovide for recirculation flow ofthe vaporized refrigerant whereby to supplement the main flow through the compressor as lrequired to prevent compressor surge, land `a lcooling conduithaving a first portion connected with a source ofY cooled liquefied refrigerant inthe refrigeration systemand with the interior of said motor casing',` asec'ond portion of said conduit being connected with the interior of Asaidfniiotor vcasing and with said recirculation conduit' to'vpass refrigerant discharged from the motor to the recirculation conduit.

5. In a refrigeration system -wherein there is substantial variation in refrigerant flow, the combination of a centrifugal compressor connected in the'system to accommodate vaporized refrigerant under variable ow conditions, a nelectric drive motor for the compressor having a fluid-tight casing, a recirculation 'conduit connected between the outlet andv inlet sides of the compressor, valve means in said conduit adapted .to provide lforAV irecirculation flow of the vaporized refrigerant whereby to supplement the main flow through the`compressor as required to prevent compressor surge, a cooling conduit having a rst portion connected'with a source of cooled liquefied refrigerant in the refrigeration system and with the interior of saidimotor casing, a second portion of said conduit being connected with the interior of 'said motor casing and with said recirculation conduit to pass refrigerant discharged fron'rthe motorto the recirculation conduit, and valve means in the first portion of said cooling conduit adapted to regulate refrigerant flou/"therethrough whereby to provide vfor a substantially constant level of superheat of refrigerant owingin said recirculation conduit downstream of the connection thereof with the second portion of saidcooling conduit. i

6. In a refrigeration system, .the combination of a refrigerant compressor of the .centrifugaltypa an electric drive motor for the compressor having a fluid-'tight casing, a compressor inlet conduit and acompressor discharge conduit, a refrigerant evaporatorconnected at its discharge side with saidcompressor inlet conduitfa refrigerant condenser connected at its inlet side'withmsaid compressor discharge conduit, a'connccting conduit between asid condenser yon` its discharge Vside and said evaporator on its inlet side, ow Varying means inone of the aforesaid conduits, `a recirculation conduit con* nected between said compressordischarge .and inlet conduits, valve'means in said recirculation conduit .adapted to provide for recirculation owwherebylto supplement the main iiow through the compressor ,as r"required to prevent compressor surge, a cooling .conduit having afzrst portion connected with 'the dischargeside ,of'tliecondenser for a supply of cooled liquified'lreffigerant and with the interiorsof said .motor casing', said conduiillyillg `a second portion connected rwith lthe interior fof `said `inottxr casing and'vvithV said recirculation conduitrtopalszs refrigerant discharged'ffrom` thei'motor tofthe recirculation Conduit. l

7. In a refrigeration system, the combination of a refrigerant compressor of the centrifugal type, an electric drive motor for the compressor having a fluid-tight casing, a compressor inlet conduit, and a compressor discharge conduit, a refrigerant evaporator connected at its discharge side with said compressor inlet conduit, a refrigerant condenser connected at its inlet side with said compressor discharge conduit, a connecting conduit between said condenser on its discharge side and said evaporator on its inlet side, iiow varying means in one of the aforesaid conduits, a recirculation conduit connected between said compressor discharge and inlet conduits, valve means in said recirculation conduit adapted to provide for recirculation flow whereby to `supplement the main iiow through the compressor as required to prevent compressor surge, a cooling conduit having a iirst portion connected with the discharge side of the condenser for a supply of cooled liqueed refrigerant and with the interior of said motor casing, said conduit having a second portion connected with the interior of said motor casing and with said recirculation conduit to pass refrigerant discharged from the motor to the recirculation conduit, and valve means in the first portion of said cooling conduit adapted to regulate refrigerant iiow therethrough to provide for cooling of the motor and cooling of the recirculating refrigerant.

8. In a refrigeration system, the combination of a refrigerant compressor of the centrifugal type, an electric drive motor for the compressor having a huid-tight casing, a compressor inlet conduit and a compressor discharge conduit, a refrigerant evaporator connected at its discharge side with said compressor inlet conduit and adapted to supply superheated refrigerant thereto, a refrigerant condenser connected `at its inlet side with said compressor discharge conduit, a connecting conduit between said condenser on its discharge side and said evaporator on its inlet side, flow varying means in one of the aforesaid conduits, a recirculation conduit connected between said compressor discharge and inlet conduits, valve means in said recirculation conduit adapted to provide for recirculation liow of superheated refrigerant whereby to supplement the main tiow through the compressor as required to prevent compressor surge, a cooling conduit having a first portion connection with the discharge side of the condenser for a supply of cooled liquefied refrigerant and with the interior of said motor casing, said conduit having a second portion connected with the interior of said motor casing and with said recirculation conduit to pass refrigerant discharged from the motor to the recirculation conduit, and valve means in the irst portion of said cooling conduit adapted to regulate refrigerant flow therethrough whereby to provide for a substantially constant level of superheat of refrigerant owing in said recirculation conduit downstream of the connec- 10 tion thereof with the second portion of said cooling conduit.

9. In a refrigeration system wherein there is substantial variation in refrigerant iiow, the combination of a centrifugal compressor connected in the system to accommodate vaporized refrigerant under variable flow conditions, an electric drive motor `for the compressor having a duid-tight casing, a recirculation conduit having a irst portion connected with the outlet side of said compressor and with the interior of said motor casing and having a second portion connected with the inlet side of the compressor and with the interior of said motor casing, valve means in the first portion of said conduit adapted to provide for recirculation flow of the vaporized refrigerant through said conduit and motor casing whereby to supplement the main flow through the compressor as required to prevent compressor surge, and a cooling conduit connected with a source of cooled liquefied refrigerant and with the iirst portion of said recirculation conduit.

10. In a refrigeration system wherein there is substantial variation in refrigerant flow, the combination of a centrifugal compressor connected in the system to accommodate superheated refrigerant under variable flow conditions, an electric drive motor for the compressor having a fluid-tight casing, a recirculation conduit having a first portion connected with the outlet side of said compressor and with the interior of said motor casing and having a second portion connected with the inlet side of the compressor and with the interior of said casing, valve means in the first portion of said conduit `adapted to provide for recirculation flow of the superheated refrigerant through said conduit and motor casing whereby to supplement the main flow through the compressor as required to prevent compressor surge, a cooling conduit connected with a source of cooled liquefied refrigerant and with the rst portion of said recirculation conduit, and valve means in said cooling conduit adapted to regulate refrigerant ow therethrough whereby to provide for recirculation of refrigerant to said compressor at a substantially constant level of Superheat.

References Cited in the le of this patent UNITED STATES PATENTS 2,080,288 McCormack May 11, 1937 2,178,425 Johnson Dec. 3l, 1939 2,247,950 Kucher July 1, 1941 2,363,273 Waterll Nov. 21, 1944 2,776,542 Cooper Jan. 8, 1957 2,891,391 Kocher .Tune 23, 1959 FOREIGN PATENTS 1,029,013 Germany Apr. 30, 1958 

